Digital Communications 2

6Study of On-line Codes for Baseband Modulation and Carrier Modulation

6.1. Objectives

In this lab work, you will study the various on-line codes for representing the binary information for its transmission on a communication channel. Two sets of codes are studied. The first provides a baseband signal. This one can be sent as it is. It can also modulate a carrier. The various digital modulations with carrier are also available (second way of transmission) and will be studied in principle and technique, especially at the demodulation level.

6.2. Description of the electronic boards

The MODICOM 5 system consists of two electronic boards. The MODICOM 5/1 board includes the conditioning of data (on-line coding) into baseband signals and, if necessary, carrier modulation and thus corresponds to the transmission part. The MODICOM 5/2 board performs the reverse operations and therefore corresponds to the reception part (see the block diagrams on the boards concerned).

The data conditioning part in baseband signals (information-to-signal coding) allows for working with the following on-line codes:

• – NRZ-L coding (level type);
• – NRZ-M coding (Mark (differential) type);
• – RZ coding;
• – Biphase coding (Manchester code);
• – Biphase-M coding (Mark);
• – Bipolar coding (also called AMI coding: Alternation Mark Inversion);
• – RB coding (Return-to-Bias);
• – Quaternary differential coding.

The carrier modulation part performs the following modulation types:

• – ASK modulation: Amplitude Shift ...